The present invention relates to a controller and method for monitoring an air system on a vehicle equipped with an air brake system and/or other air controlled systems. Air brake systems are efficient means of providing braking power to heavy vehicles, especially separable vehicles such as tractors and trailers. However air systems are prone to leakage and air flow obstructions due to the multiple valves and the potentially long connections between the valves. Compressor operation may degrade over time without warning and affect the air pressure available to the braking system. There is a desire to have an efficient method to monitor the air system operation for any leakage, obstruction, component degradation or other problems that may affect air system effectiveness.